I tried it two years running.  I covered the bottom boards with  hardware 
cloth up to about 3" of the access where I placed a 1/2" square across  the front 
edge of the wire  to block the bees.
 
The diatomaceous earth caked up pretty fast due to humidity I suppose. Any  
way there was no evidence that it deterred mites one little bit.
 
Out of some 16 hives 15 simply absconded.  The remaining hive was one  that 
was so hot they would "sew up your pants leg".   I started over  with help from 
a nearby commercial beekeeper.
 
George Williams
FL

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